Greenhouses are horticulture facilities covered with glass windows at the whole area. In greenhouses covered mainly with a transparent plate glass, glass breakage is dangerous to workers because the shattered pieces of glass mix with the soil in greenhouse. Glass has had further problems in that since glass has high transmittance to sunlight and high heat conductivity, the temperature inside greenhouse becomes very high in the daytime in summer, requiring a high cost for cooling and to the contrary, in the night in winter, the temperature inside greenhouse becomes low owing to radiational cooling, requiring a cost for heating.
In order to solve these problems, it has been conducted to attach, to the glass windows of greenhouse, a film for prevention of scattering of broken pieces of glass, or a sunlight-control film having a metal or metal oxide layer formed by vapor deposition (i.e. a heat ray-reflecting film).
For example, greenhouses having a heat ray-reflecting film attached to the glass of the lighting area thereof are proposed in JP-A-54-66227, JP-A-61-58527 and JP-A-61-58528. These proposals, however, have a main object of reducing the energy (e.g. fuel oils) required for the heating of greenhouse inside, and make no suggestion on any persistent and effective means for prevention of growth of the waterdrops formed by dew condensation.
With these film-attached glass windows, there has been a problem in that dew condensation takes place owing to the difference in temperature between greenhouse inside and outside, at the side of window facing the inside of greenhouse, i.e. at the film side of window, and it hinders the transmission of sunlight or induces the falling of waterdrops from the greenhouse ceiling, giving adverse effects on horticulture crops.
In order to solve this problem, it has been conducted to coat a surfactant on the film surface of window facing the inside of greenhouse. However, this approach had no persistent effect and had no practical applicability.